Santy asked:

Is it possible to add into a naturalistic philosophy (naturalism) the existence of immaterial things? And, Is it possible that, though God did not exist, could immaterial things, even exist?

Answer by Massimo Pigliucci

One of the issues with the philosophical position of naturalism is that it means different things to different people, and those differences hinge precisely on the ontological status of immaterial, i.e., non physical, entities.

To begin with, let us distinguish among three positions to help frame the discussion: physicalism, naturalism and supernaturalism. At one end of this rough ontological spectrum, physicalism is the idea that only physical things, made of matter/ energy, exist in any meaningful sense of the word ‘exist.’ At the other end of the spectrum, supernaturalism is the position that not only there are physical things, but there exist also entities (one or more) that transcend nature, i.e., that violate, or are somehow outside of, the laws of nature as understood by science.

Somewhere in the middle – though closer to physicalism – are a variety of forms of naturalism. One type of naturalism may recognize the existence of only physical objects, which means that it collapses into physicalism (or perhaps it would be better to say that physicalism is one extreme kind of naturalism). But there are naturalists who consider themselves to be mathematical Platonists, and who propose that mathematical structures (i.e., abstract entities such as numbers, geometrical figures, theorems, etc.) have a mind-independent ‘existence,’ and they are therefore discovered (as opposed to invented) by mathematicians. This existence, of course, isn’t of the same type as that of physical objects (nobody thinks one can discover mathematical objects by using a telescope), but it is nonetheless more than the result of arbitrary abstractions of the human mind.

(By contrast, Sherlock Holmes – also an abstract entity – does not ‘exist’ in this sense, as he was arbitrarily invented by Arthur Conan Doyle during the 19th century: ‘truths’ about Holmes can only be ascertained by consulting Conan Doyle’s novels, while truths about mathematics can be independently discovered, and verified, by anyone in the world with sufficient mathematical skills.)

There are at the least two other varieties of naturalism worth mentioning. Both are more radical then the ones we have seen so far, but in very different ways.

David Kellogg Lewis, for instance, proposed a notion nowadays known as modal realism, the idea that all (logically) possible worlds are just as real as our world. These worlds, according to Lewis, are isolated from each other, and not causally connected among themselves. If this sounds weird, note that the notion isn’t that different from one way to look at quantum mechanics, the aptly named many-worlds (or Everett’s) interpretation, according to which every time a decision – say, to get chocolate rather than vanilla ice cream – is made in our world the universe ‘splits’ into two diverging universes: in one I picked chocolate, and in the other ‘I’ picked vanilla (the second universe seems rather less interesting to me, I must say…). This is not the same, although according to physicist Sean Carroll is related to, the notion of a multiverse in cosmology.

The second type of radical naturalism actually eschews physicalism, in a sense. It is known in philosophy of science as Ontic Structural Realism (OSR), and it is championed by philosophers like James Ladyman and Don Ross (see their book, ‘Every Thing Must Go’). According to OSR, which its supporters claim to be derived at the least in part from contemporary physics’ best understanding of the deep structure of reality, the universe is not made of ‘things,’ be they people, stars, or subatomic particles, but only of ‘relations,’ or ‘structures.’ It is these structures that are, according to the structural realist, described by modern physical theories like quantum mechanics.

Needless to say, all these forms of naturalism have their critics, but my sense is that most professional philosophers these days are naturalists of one type or another.


Answer by Geoffrey Klempner

In answer to your question, Santy, let me propose a theory. It is not a theory in which I believe, that is to say, I don’t know of any convincing empirical evidence in support of this theory. However, it is a theory that could be true – or at least believable – were sufficient evidence to be uncovered.

I shall call the theory, ‘naturalist dualism’. That is intended as a clue. According to naturalist dualism, nature consists of two kinds of causally effective substance or entity: material substances and immaterial substances. (Numbers and abstract objects would not be included under the heading ‘immaterial substances’ because they do not stand in causal relations, although there are some varieties of Platonism that embrace the idea that our minds in some extended sense ‘causally’ interact with numbers, etc.)

According to naturalist dualism, minds are immaterial substances much as Descartes conceived them. They lack any of the essential attributes of material substance, such as mass or physical dimension. Because of this, they are incapable of being investigated by science, which relies on physical apparatus and instruments. What distinguishes naturalist dualism from Cartesian dualism, however, is that immaterial substances are not conceived as having been created by a supernatural being. They are simply part of the furniture of the given universe, the part that you and I can see by looking into ourselves, but which cannot be accessed by the physical methods of science.

It would be a bold person who claimed that there was any part of the universe that is necessarily inaccessible to the methods of science. But it is not such a nutty idea either. Thomas Nagel argues a version of this claim (weaker than I am claiming here) in his well-known article ‘What Is It Like to Be a Bat?’.

If the universe contains such immaterial substances, then it ought to be possible to detect this indirectly by means of experiments revealing gaps in the causal order, where previously we were not aware of any such gaps. For example, a better understanding of the physical workings of the brain might reveal that it works more like a relay mechanism than a biological computer, receiving and processing impulses from an unobservable source.

Would this be a vindication of Descartes? Interestingly, no, because the very same ‘evil demon’ thought experiment that Descartes runs for the physical world – the world of material objects – can also be run for the world of material and immaterial objects. I know for certain that I exist, but I don’t know (because I might be deceived by an evil demon) that any material OR immaterial substances exist.